An interferometric wavefront sensor employing phase-shift interferometry typically consists of a light source that is split into two wavefronts (e.g., a measurement and test wavefront) that are later recombined after traveling different path lengths (e.g., reference and test/measurement arms). Phase-shifting interferometry (PSI) can be used to accurately determine the phase differences and, for example, the corresponding profile of the surface under examination. With PSI, the optical interference pattern is recorded for each of multiple phase-shifts between the reference and measurement wavefronts to produce a series of optical interference patterns that span at least a full cycle of optical interference (e.g., from constructive, to destructive, and back to constructive interference). The optical interference patterns define a series of intensity values for each spatial location of the pattern, wherein each series of intensity values has a sinusoidal dependence on the phase-shifts with a phase-offset equal to the phase difference between the combined measurement and reference wavefronts for that spatial location. The phase-shifts in PSI can be produced by changing the optical path length from the measurement surface to the interferometer relative to the optical path length from the reference surface to the interferometer.
While PSI is an established method for measuring a variety of physical parameters, current systems are generally unsuitable for performing fast, continuous measurements of transient optical phenomena such as chemical diffusion, crystal growth, and measurements of rapidly varying object temperatures. Accordingly, phase-shifting interferometers incorporating micro-machined components, in conjunction with innovative phase-shifting techniques, are needed to rapidly and continuously measure transient phenomena.